1. Technical Field
The present invention relates to an inspection method for an array substrate used in a liquid crystal display apparatus and an inspection device for the same, more particularly to a disconnection inspection method for storage capacitor lines on a TFT array substrate and a disconnection inspection method for the same.
2. Prior Art
As shown in FIG. 8(a), in a thin film transistor (TFT) array substrate, signal lines 15 and gate lines 21 are wired in the form of matrix on a glass substrate while crossing to each other in an electrically nonconductive state, and TFTs 22 are arranged in the vicinity of cross portions thereof. The above-described gate line 21 and signal line 15 are respectively connected to a gate and a source of a TFT 22. A transparent electrode (ITO) is connected to a drain of the TFT 22. A storage capacitor electrode 25 is arranged so as to be opposite to a specified portion 23 of the transparent electrode, and a storage capacitor (Cs) 24 is constituted of the specified portion 23 of the transparent electrode and the storage capacitor electrode 25. In the case of a storage capacitor system, the storage capacitor electrode 25 is connected to storage capacitor drives circuit through a storage capacitor line (hereinafter referred to as a Cs line) 13. An arrangement of the respective lines and electrodes or the like described above on the TFT array substrate is performed by repeating a patterning process on the glass substrate.
In recent years, a length of each of the above-described lines has become longer owing to a larger screen of the liquid crystal display apparatus, and each of the above-described lines has become thinner owing to high definition of the liquid crystal display apparatus. This results in a higher probability of occurrence of defective articles due to a line disconnection or the like, when the above-described patterning process forms each line. Therefore, an inspection of the TFT array substrate is performed to prevent the defective articles from entering the subsequent manufacturing process in the case where the defective articles occur. For the inspection, a TFT array tester generally available in a market is used. The TFT array tester is capable of inspecting a disconnection (open circuit), a short circuit and a defective resistance of each line, a pixel defect or the like.
In the disconnection inspection of each line by using the above-described TFT array tester, using the above-described TFT array tester has not performed the disconnection inspection for the Cs line 13. This is because the Cs line 13 is short and defects of the Cs line 13 due to disconnection are difficult to be detected even if a lighting test is executed for a small panel of 12 inch diagonal or less using the storage capacitor system, and because a structure shown in FIG. 9(a) without the Cs line 13 (drive capacitor system) is adopted in most liquid crystal display panels of 14 inch diagonal or larger. Since this drive capacitor system does not wire the Cs line 13, there are advantages that the probability of occurrence of defective articles is reduced and an aperture ratio of the liquid crystal display apparatus is improved.
However, when the liquid crystal display has higher definition and a larger size, wiring of the gate line 21 becomes longer and a line width thereof becomes thinner, resulting in a larger resistance of the wiring. Moreover, since the number of the signal lines 15 is large, capacitance at a cross portion of the signal line 15 and the gate line 21 increases. As a result, a load to a gate driver outputting a gate drive signal becomes larger. Furthermore, in the drive capacitor system, since the storage capacitor electrode 25 of the storage capacitor 24 is connected to the gate line 21 of a front or rear step thereof, both of the gate signal and the signal to the storage capacitor electrode 25 exist mixedly in the gate line 21, and a quantity of charges that can be stored in the storage capacitor 24 is relatively small in comparison with the storage capacitor system.
Because of the reason described above, recently in the liquid crystal display panel of 14 inch diagonal or larger, the storage capacitor system using the Cs line 13 as shown in FIG. 9(b) has been increasingly adopted. Therefore, when the storage capacitance system is used in the liquid crystal display panel of 14 inch diagonal or larger, the Cs line 13 is included. Accordingly, if the Cs line 13 is disconnected, the disconnection of the Cs line 13 is detected by the lighting test. However, the lighting test is performed after the liquid crystal display panel is assembled. Therefore, it is more waste less and preferable that the disconnection of the Cs line 13 be detected at a stage where TFT array substrates are manufactured, and that defective TFT array substrates are not allowed to enter the subsequent process.
The TFT array tester inspecting a disconnection, a short circuit and a defective resistance of each line, a pixel defect or the like of the TFT array substrate cannot detect the disconnection of the Cs line 13. The tester supplies a pulse signal Vd as shown in FIG. 10 to the signal line 15 while supplying a constant voltage Vcs to the Cs line 13. By supplying the constant voltage Vcs to the Cs line 13, the voltage Vcs is applied to the storage capacitor electrode 25. Note that, in the above-described pulse signal Vd, since the falling of the pulse signal Vd occurs after the gate signal is turned off, and does not have a relation to a potential difference in the storage capacitor 24, the pulse signal Vd falls in an optional time.
And, as shown in FIG. 10, the gate signal is applied from the gate line 21 to the TFT 22 at the time t0 to turn the TFT 22 to an ON state, thus the pulse signal Vd is applied from the signal line 15 to the specified portion of the transparent electrode 23 of the storage capacitor 24 having a capacitance of C. Moreover, at the time t1, the TFT 22 is turned to an OFF state by turning off the gate signal. When the voltage of the pulse signal Vd at this time is set as Vd1, the voltage at the specified portion of the transparent electrode 23 becomes Vd1. With regard to a potential difference between the specified portion of the transparent electrode 23 of the storage capacitor 24 and the storage capacitor electrode 25 after the time t1, a difference between the voltages Vcs and Vd1, is maintained, and a quantity of charges Q1 stored in the storage capacitor 24 becomes C coulomb (Vcs-Vd1). Thereafter, the gate signal is applied to the TFT 22 to turn the TFT 22 to an ON state. Then, the quantity of charges Q1 stored in the storage capacitor 24 is detected by a reading circuit of the TFT array tester.
However, since the voltage Vcs supplied to the Cs line 13 is a constant voltage, when the pulse signal Vd from the signal line 15 is not applied to the storage capacitor 24, the voltage of the specified portion of the transparent electrode 23 is 0V, and the potential difference between the specified portion of the transparent electrode 23 of the storage capacitor 24 and the storage capacitor electrode 25 becomes Vcs. At this time, a quantity of charges Q2 stored in the storage capacitor 24 becomes CVcs coulomb, and the quantity of charges Q detected by the TFT array tester becomes CVd1, coulomb that is a difference between Q2 and Q1. Therefore, this indicates that the quantity of charges Q is determined by writing voltages from the storage capacitor 24 and the signal line 15, and that an influence of the disconnection of the Cs line 13 is not considered.
In addition, Japanese Patent Laid-Open No. Hei 11(1999)-84420 discloses a detection method, in which resistance of each type of line is calculated by measuring a voltage and a current in each kind of line and a disconnection or a short circuit is detected by the calculated resistance values. However in this method, pads for connecting probes are required to be provided to the respective Cs lines, and the number of pads increases.
The present invention is directed to an inspection method for inspecting a disconnection of storage capacitor lines on a TFT array substrate simply in a short time and an inspection device for the same.
The gist of the inspection method for an array substrate according to the present invention is an inspection method for an array substrate, in which the array substrate includes: a substrate; a plurality of gate lines, a plurality of signal lines and a plurality of storage capacitor lines, which are disposed in an electrically nonconductive state on the substrate in the form of matrix; a plurality of switching elements electrically connected respectively to the plurality of gate lines and the plurality of signal lines; and a plurality of storage capacitors electrically connected respectively to the plurality of storage capacitor lines and the plurality of switching elements, the inspection method comprising the steps of: applying pulse signals from the plurality of storage capacitor lines to the plurality of storage capacitors; applying pulse signals from the plurality of signal lines to the plurality of storage capacitors via the plurality of switching elements; and measuring quantities of charges stored in the storage capacitors based on potential differences between the foregoing two types of pulse signals. If only the pulse signals from the foregoing signal line are applied to the foregoing storage capacitors, an influence of the disconnections of the foregoing storage capacitor lines is not considered when the quantities of charges stored in the storage capacitors are measured. In order to consider the influence of the disconnections of the foregoing storage capacitor lines, the pulse signals are also applied to the foregoing storage capacitor lines when the pulse signals are applied from the foregoing signal lines. Thus, the quantities of charges stored in the foregoing storage capacitors are determined by the pulse signals applied from the foregoing signal lines and storage capacitor lines, and the disconnections of the foregoing storage capacitor lines are detected when the quantities of charges stored in the foregoing storage capacitors are measured.
The gist of the inspection device for an array substrate according to the present invention is an inspection device for an array substrate, in which said array substrate includes: a substrate; a plurality of gate lines, a plurality of signal lines and a plurality of storage capacitor lines, which are disposed in an electrically nonconductive state on the substrate in the form of matrix; a plurality of switching elements electrically connected respectively to the plurality of gate lines and the plurality of signal lines; and a plurality of storage capacitors electrically connected respectively to the plurality of storage capacitor lines and the plurality of switching elements, the inspection device comprising: a pulse signal generating device connected to the storage capacitor lines and the signal lines in order to apply the pulse signals respectively to the plurality of storage capacitors; and a circuit for measuring the quantities of charges stored in the respective storage capacitors. By connecting the foregoing pulse signal-generating device to the foregoing signal lines and the storage capacitor lines, the pulse signal are applied to the foregoing storage capacitors from the signal lines and the storage capacitor lines. Thus, the disconnections of the storage capacitor lines can be detected by measuring the quantities of charges stored in the storage capacitors through a circuit for measuring the foregoing quantities of charges.